Method for finishing the ball cup of a homocinitic joint

ABSTRACT

The invention relates to a method for finishing the ball cup of a homocinitic joint, especially for motor vehicles, having a ball ring-shaped bearing surface for the ball cage and a plurality of essentially axial running guideways which interrupt said ball ring-shaped bearing surface. The guideways are provided for the balls which are arranged in the ball recesses of the ball cage and which transmit torque between the ball cup and the ball star. In order to be able to finish such ball shells quickly, economically and as fully automatic as possible, the invention provides that both the ball ring-shaped bearing surface for the ball cage as well as the guideways for the balls are produced by means of a turning machining.

TECHNICAL FIELD

The invention concerns a process for finish-machining the bearing casingof a constant-velocity joint, especially for automobiles, with aspherical bearing surface for the bearing cage and a plurality of guidetracks that basically run axially and interrupt the spherical bearingsurface for the bearings transmitting the torques between the bearingcasing and the bearing star arranged in the pocket of the bearing cage.

BACKGROUND OF THE INVENTION

In automobiles with front-wheel drive, the front wheels are driven byjoints. Therefore, front-wheel axle shafts must have joints that allowthe wheels both to spring in and out, and also to lock.Constant-velocity joints (homokinetic joints) are used to make thewheels drive as steadily as possible. Fixed constant-velocity jointsdesigned as cap joints are used for joints on the front axle shafts,inter alia, while for joints on the rear axle shafts movingconstant-velocity joints designed as cap joints are used that allowaxial movement in addition to flexure of the joint.

These cap joints are comprised of a bearing star set on the wheel end ofthe axle shaft, on which the bearing cage with its bearings and thebearing casing connected to the wheel driveshaft sit. On a fixedconstant-velocity joint, the bearing casing and star have curved trackson which the bearings move. On a moving constant-velocity joint, thetracks on the bearing casing and star are designed to be even.

On the constant-velocity joints comprised of a bearing star, bearingcage and bearing casing that are known in practice, the finish-machiningof the bearing casing, which has a bearing surface for the cage andguide tracks for the balls, takes a large number of different steps,which are sometimes done on different machines. Starting from adrop-forged bearing-casing blank, in the known finish-machining methods,the guide tracks are produced by broaching and/or milling and finalgrinding, while the bearing surface is produced by turning. Machining isvery expensive, especially finish-machining bearing casings of fixedconstant-velocity joints, because both the bearing surface and the guidetracks are designed to be curved in the axial direction of the bearingcasing.

The disadvantage of this known production method is that becausedifferent machine-tooling methods are used, in which the bearing casingbeing machined must be transformed many times and potentially fed todifferent machines, it is very time-consuming and hence expensive tofinish-machine the bearing casing. What is more, because of the varioustransformations, defects occur so that tolerances are only possiblewithin certain limits.

SUMMARY OF THE INVENTION

The problem of the invention is to provide a method of finish-machiningthe bearing casing of a constant-velocity joint so that bearing casingscan be finish-machined in a simple, inexpensive way that can be fullyautomatated with high precision.

The invention solves this problem by producing both the sphericalbearing surface for the bearing cage and the guide tracks for thebearings by a turning operation.

This production method in the invention makes it possible, for the firsttime, to make the bearing casing of a constant-velocity joint by auniform machine-tooling method, namely a turning operation method, wherethe turning occurs after the chucking of the blank of a bearing case. Asa result of machining only by the turning operation on a machine, themethod in the invention has a clear advantage in terms of time, cost andprecision over the finish-machining method known in practice.

One practical embodiment of the invention proposes that the axial courseof the guide tracks be designed purely spherically.

The invention also proposes that the axial course of the guide tracks becomposed of a cylindrical part and a spherical part. Both sorts ofbearing casings are used for fixed constant-velocity joints.

The invention also proposes that the guide tracks can run eitherparallel to the axis or at a sharp angle to the axis of rotation of thebearing casing.

In one practical embodiment of the invention, the tangents of the ballswith the accompanying guide tracks run spatially parallel to oneanother. In particular, the design of the spherical guide tracks alsoproposes that the distance between the tangents of the balls and theaccompanying guide tracks change in the axial direction, which optimizesthe transmission of torque.

One special embodiment of the invention proposes that the bearing casinghave a polygonal opening on the bottom to connect it to the wheeldriveshaft. The design of this polygonal opening for the wheeldriveshaft makes it possible to design the bearing casing as a standardcomponent for different constant-velocity joints, since the respectivedrive can be adjusted via the wheel driveshaft made as a separatecomponent. It is also easier to manufacture a bearing casing without awheel driveshaft molded onto it. In one advantageous embodiment of thisbearing casing, the polygonal opening is designed to be conical in theaxial direction. This conicity of the polygonal opening permitsself-centering of components being connected to one another.

Lastly, the invention proposes that bearing casing and wheel driveshaftbe designed as a one-piece component and the rotary method be a hardrotary method, so that even hardened workpieces can be machined.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the invention will emerge from thefollowing description of the accompanying drawings:

FIG. 1 illustrates a schematic design of a fixed constant-velocity jointwith a bearing casing machined according to the invention; and

FIG. 2 illustrates a method of finishing a bearing casing.

DETAILED DESCRIPTION OF THE INVENTION

The fixed constant-velocity joint 1 shown is comprised of a bearing star2 set on the wheel end of the axle shaft via teeth 2 a, on which abearing cage 3 with bearings 4 and a bearing casing 6 connected to awheel driveshaft 5 sit.

On the constant-velocity joint, designed as a fixed constant-velocityjoint 1, the bearing casing 6 and the bearing star 2 have sphericallycurved guide tracks 7, on which the bearings 4 move. The bearing casing6 has a spherical bearing surface 8 for mounting the bearing cage 3.

In the example of the embodiment shown, the tangents 9 of the bearingcasing 6 run spatially parallel to one another on the accompanying guidetrack 7.

In the example of embodiment of a fixed constant-velocity joint 1 shown,the bearing casing 6 and the wheel driveshaft 5 are designed as separatecomponents. To connect the bearing casing 6 to the wheel driveshaft 5,there is a polygonal opening 10 in the base of the bearing casing 6,into which the wheel driveshaft 5 can be inserted, with a polygonalprojection molded on accordingly. To make these adjacent polygonalsurfaces self-centering, the polygonal opening 10 and the polygonalprojection on the wheel driveshaft 5 are designed to be conical in theaxial direction.

The part of the wheel driveshaft 5 pointing away from the bearing casing6 is comprised of a cylindrical part 5 a for the wheel bearing and aconnecting part 5 b to connect it to the wheel being driven. Thisconnecting part 5 b can have, for example, a polygonal outer contour orteeth on the outside.

Unlike the example of embodiment shown, it is obviously also possible todesign the bearing casing 6 and the wheel driveshaft 5 as a one-piececomponent.

Referring to FIGS. 1-2, a method of finishing a bearing casing isillustrated. The method includes clamping the blank of a bearing casing6 in the chuck 19 of a machine (e.g., a lathe 20) and producing thespherical bearing surface 8 for the bearing cage 3 as well as the guidetracks 7 for the bearings 4 with a cutting tool 21 by a turningoperation 30. As a result of machining only by the turning operation ona machine, the method in the invention has a clear advantage in terms oftime, cost and precision over the finish-machining method known inpractice.

What is claimed is:
 1. A method of finish-machining a bearing casing ofa constant-velocity joint with a spherical bearing surface for a bearingcage and a plurality of guide tracks that basically run axially andinterrupt the spherical bearing surface, for balls arranged in bearingpockets of the bearing cage transmitting torque between the bearingcasing and a bearing star, wherein both the spherical bearing surfacefor the bearing cage and the guide tracks for bearing are produced onlyby a hard rotary turning operation, the turning operation is carried outin a single chucking position.
 2. The method according to claim 1,wherein the axial course of the guide tracks is designed to be purelyspherical.
 3. The method according to claim 1, wherein the axial courseof the guide tracks is composed of a spherical part and a cylindricalpart.
 4. The method according to claim 1, wherein the guide tracks runparallel axially.
 5. The method according to claim 1, wherein the guidetracks run at a sharp angle to the axis of rotation of the bearingcasing.
 6. The method according to claim 1, wherein the tangents of thebearings run parallel to one another spatially with the accompanyingguide tracks.
 7. The method according to claim 1, wherein the distancebetween the tangents of the bearings and the accompanying guide trackschanges in the axial direction.
 8. The method according to claim 1,wherein the bearing casing has a polygonal opening in its base toconnect it to a wheel driveshaft.
 9. The method according to claim 8,wherein the polygonal opening is designed to be conical in the axialdirection.
 10. The method according to claim 1, wherein the bearingcasing and the wheel driveshaft are designed as a one-piece component.